Roller hearth furnace



Dec. 27, 1949 S. M. STOLER ROLLER HEARTH FURNACE Filed Jan. 2 6, 1949 2Sheets-Sheet l lNvEN-roR SAMUEL M. STOLER ATTORNEY Dec. 27, 1949 s. M.s'roLER ROLLER HEARTH FURNCE 2 Sheets-Sheet 2 Filed Jan. 26, 1949nwENToR SAMUEL M. STOLER j? l @A1-Tor@ Patented Dec. 27,

Samuel M. Stoler, Norristown, Pa., asslgnor to R-S Products Corporation,Philadelphia, Pa., a corporation of Delaware.

A Application January-zc, 1949, semi Np. 72,815

' rc1. 26a-4o) 15 Claims.

The rollers are ,of either solid or tubular con-- struction, with theshafts extending through and journalled in or laterally beyond the sidewalls of the furnace, with externally applied power effective to rotatethe rollers. Such power application is either individual to therespective shafts, or in groups from a common power source.

There are usually a plurality of such rollers in general planaralignment longitudinally of the furnace, and they may coact with rollersoutside `of and longitudinally beyond the furnace to feed work of anydesired sort into the furnace entrance, through the furnace, and outthrough the discharge end or exit at the opposite end of the furnace. ,f

As the furnaces have previously been constructed the rollers within thefurnace have been more or less directly exposed, either to direct burnernames' in the case -of fuel-fired furnaces, or to radiation within thefurnace in the case of vfuel-fired or electrically heated furnaces,`sothat it has generally .been impossible to elevate the temperatures ofthe Work without also deviating the temperatures of the rollers topractically the same magnitude. In some instances the tubular types ofrollers have been used as conduits for a coolant owing therethrough, andin such cases reliance has necessarily been upon continuous flow of theinternal coolant for dissipation of the heat absorbed by the rollers.Thisl form of cooling also effects a limitation upon the heat availablefor incidence upon the work.

It is well known in the art that the various metals of which rollershave been previously made, lose their strength and tend to disintegrateunder elevated temperatures. Rollers made of refractory materials havelikewise proven unsatisfactory under elevated temperatures due to theirfrangibility and friability. Combinations of metals and refractories inroller construction have not been very eiectlve in permitting attainmentof elevated furnace temperatures without an inherent shortening ofroller life. As replacement of a roller involves shutting down thesituation also place sharp limitations upon the maximum furnacetemperatures in order to effect long periods of continuous furnace use.

For these and related reasons, the conventional .roller hearth furnaceof present commercial acceptance is not capable of furnace temperatureshigher than about of the order of 2100 F. This limitation restricts theutility of the furnaces. requires the use of larger furnaces than wouldotherwise be necessary. and necessitates the use of other types offurnaces when the work must be brought .to higher temperatures than suchillustrative maximum.

It is among the objects of this invention: to improve the art of rollerhearth furnaces; to provide a' roller hearth furnace with rollers insuch relation to partial partitions in the furnace as to be shieldedkfrom direct incidence of the hot gases, and also from radiation fromthe furnace, while still being effective to support and advance the workunder higher furnace temperatures than has previously .been attainable;to provide a roller hearth furnace with an air-cooling system forcooling the rollers without yany appreciable adverse eects on the worksupported thereon; to utilize the velocity of eillux gases .as

they vent from the furnace to induce a cooling stream of air across andagainst the rollers in a roller hearth furnace; to provide a rollerhearth furnace with a high thermal head by which the work can be quicklyheated to a desired working temperature within a short time interval; topro- A vide r, furnace and roller assemblyin which the hot gases are incontinued contact with the work While still aifording eillcient aircooling for the conveying rollers; to provide a roller hearth furnace inwhich the temperatures incident on the work are appreciably above theorder of 2100 F.; to provide a roller hearth furnace with shieldingdevices to protect the transverse rollers from direct or indirect heatfrom the furnace except for an axially short peripherally small areaextending above the shield far enough to support the work out of contactwith the shield; to provide a roller hearth furnace with rollers of atransverse extent adequate to support and convey or advance work ofvarious sizes to a given maximum with a directed cooling air streamconfined to and accelerated against and past the exposed transverseportion of the rollers; to provide a positive `flow of air againstrollers in a roller hearth furnace for cooling same; and other objectsand advantages will become apparent as the description proceeds.

furnace, it will be clear that the economics of the Il In carrying outthe invention in an illustrative embodiment, there is provided acontinuous roller hearth furnace of any desired length, with a pluralityof shielding, semipartitions in longitudinally spaced transversedisposition. The partial partitions define a combined roller housing andshielding structure, and a vertical channel for cooling air leadingexternally about the rollers adjacent to the work-supporting portionsthereof.

Preferably, as the only vents for the products of combustion other thanthe end openings of the furnace, vent devices are disposed in thegeneral plane of the partitions so that the accelerated velocity of thehot furnace gases in venting induce a flow of cooling air through thepartitions in scouring relation to the rollers. Preferably also, theintakes for the vents are disposed inwardly of the furnace generallycontiguous to the work so that the heated gases moving to the vents areforced into scouring relation to the work. As a modification thereof thevents are provided in pairs or other pluralities in order to stillfurther increase or enhance the scouring of the work by the hot furnacegases. The furnace is designed to rapidly heat work to elevatedtemperatures, appreciably greater, if desired, than the illustrative2100 F. The work may comprise any elongated articles, whether tubes,bars, billets, blooms. rods, sheets, or smaller articles carried intrays or other subsupporting means. One illustrative application of theinvention, for instance, is for the heating of elongated bars fordelivery adjacent to a forging or other working device as shown in myapplication for patent, Serial Number 29,616, led May 27, 1.948.

In the accompanying drawings forming part of this description:

Fig. 1 represents a fragmentary side elevation,

partially in fragmentary longitudinal vertical section, of one form ofthe invention, remote from either end of the furnace, with the externalframing and bracing removed for purposes of clarity.

Fig. 2 represents a transverse vertical section therethrough taken online 2-2 of Fig. l.

Fig. 3 represents a transverse vertical section therethrough taken online 3-3 of Fig. 1.

Fig. 4 represents a fragmentary longitudinal vertical section through amodied form of furnace, having two parallel transversely spaced vents.

Fig. 5 represents a transverse section through the furnace of Fig. 4. YK

Fig. 6 represents a fragmentary longitudinal section through a furthermodified form of roller .u

hearth furnace, in which a positive flow of cooling air is provided forimpact against the roller. Fig. 7 represents a transverse sectionthrough the furnace of Fig. 6.

Fig. 8 represents a side elevation. partially in section, of a furnaceaccording to this invention, showing the end wall constructionv thereof.

Fig. 9 represents an end elevation of the complete furnace, showing theend Wall and the aperture therein to receive the work fed across theouter or external rollers of the furnace.

Referring to Figs. 1,2, and 3, the furnace I 0 comprises a singlefurnace chamber I I, defined 4 and supporting structures and framing.The bottom wall I5 preferably has a lower clearance or spacing I6, fromthe ultimate support, in order to provide air flow passagescommunicating with the cooling slots to be described, althoughlongitudinal air flow is not in any degree essential to the functioningof the furnace. Usually, therefore, this space will receive framingmembers. The bottom wall I5 and portions of the side walls I 3 and Il ofthe furnace are interrupted transversely by the respective compoundpartitions I1, each extending between the bottom wall and vertically.along the side walls I3 and Il to a' horizontal upper edge a littleabove the center of the vertical height of the furnace chamber II. Thepartitions Il are each formed by spaced walls I8 and 20 preferably, butnot essentially, vertical, connected at their upper edges by ahorizontal wall or web 2 I. The horizontal wall 2| delineates thehorizontal upper edge of the partitions located slightly above thevertical middle of the furnace, and, because of its central opening tobe described, forms a partial closure for the vertical air channel 22formed by the space between the contiguous surfaces 23 of wall I8 and 24of wall 20. Channel 22 ls'open on part of the side walls and across thebottom of the furnace in a peripherally continuous entrance. It isincomplete or partial because in the substantial center of the furnacethe partition wall 2l is cut away vertically in transverse verticallyextending generally parallel spaced surfaces 28 and 30 extendinglongitudinally of the furnace, and the complemental partition walls I8and 20 are cut away vertically and horizontally and forms with theopening in the horizontal web 2l a longitudinal horizontal slot 29 inthe partition. Slot 29 is defined in walls I8 and 20 and closure 2I bythe horizontal bottom edge surfaces 25 and the vertical side edges 26and 21, and the vertical edges 28 and 30 of the upper wall portion 2land is generally symmetrical of the longitudinal axis in the center ofthe furnace. As the upper partition wall 2I is cut all the way throughand the partition walls I8 and 20 are cut below the upper wall, it willbe observed that the slot 29 is in communication with the space 22, andthe latter extends laterally out of both sid of the furnace and incommunication with the lower passage I6, if the latter is provided, sothat air passing into the furnace from the exterior thereof passes intothe'channel 22, and thence into the restricted slot 29, in which it isdrawn upwardly under high acceleration by means to be described. It willbe observed that the partition wall surfaces, respectively 3l onpartition wall I8 opposite to channel surface 23 thereof, and 32 onpartition wall 20, opposite to channel surface 24 thereof, definerespectively adjacent effective ends of a pair of contiguous partialchambers, each of which is completed by the complemental facing surfaceof the adjacent partition. The furnace is therefore provided with aplurality of partial chambers, as illustratively 33, 3l. 35, 36, etc.,continued as desired for the length of the furnace. although being onlypartial, as the upper portion of all of the partial chambers is acontinuous straight-through single furnace chamber.

by the upper wall I2, side walls I3 and Il, and

bottomfwall I5. It willbe understood that end walls 63 having openings64 corresponding in dimension generally to the slots 29 to be described,will be provided as shown in Figs. 8 and 9. The furnace will beconstructed in any desired manner, as to refractories. insulation, andreinforcing Although I may use any form of heating that may be desired,it is preferred to use fluid fuel such as gas or oil, and this isintroduced through burner openings in the furnace. Illustratively andpreferably, I provide a burner opening 31 low in side wall I3. and anadditional burner 38.high

75 in the opposite side wall Il. Preferably these any desired numbers ofburners, and independent or dependent controls thereof may be used ascircumstances require.

In order to support and advance the work, a series of conveyor rollers40 are provided, preferably as cylindrical shafts according in numberwith the number of partitions, extending across and out of the furnacelaterally in order to be driven externally, as by sprockets 4l, drivenby individual or common power means. Additional rollers 40 are providedexternally of the end walls, as shown in Figs. 8 and 9. The shafts aresuitably journalled on the frame of the furnace, and are each disposedin the respective channel space 22 of the partitions beneath the upperclosures 2l thereof, and extending across and partially into thelongitudinal slots 29 of the partitions, with the upper peripheral edgeof the roller 40 extending just above the bottom horlzontal'edge 25 ofthe slot. Although the preferred form of roller is a cylindrical shaft,it will be understood that the shaft may be of smaller diameter anddropped a little further down and an actual roller may be mounted on theshaft in centered and intersecting relation to the slots in thepartition. If desired, the shafts 40 may be ,tubular and associated withany desired sort of fiuid coolant passing internally thereof as iscommon in the art to augment or amplify the cooling by the external airflow to be described.

An important feature of the invention is the controlled exhaust of thewaste gases forming the products of combustion.Y This is accomplished byproviding vent openings in the furnace at carefully selected points orareas, asv preferably the only vents in the furnace other than the endapertures through which the bars of metal are fed and delivered,although if desired additional vents can be used at other points, andthe whole venting system controlled to secure the'results to beexplained. A simple structural procedure isv the mere formation of ventapertures in the roof of the furnace as indicated at 49, permitting theexhaust directly into the room containing the furnace. It is preferred,however, to provide actual stacks, such as 42, having sealing flanges .sy stacks or vents, in respective asymmetry with the vertical center lineof the furnace, even if need be in the side walls of the furnace, it ispreferredl that the center line or axis thereof lie in said transversediametric plane containing the center line of the air channel 22transversely of the furnace. With the stacks or vents disposed as singleopenings, or asplural related openings transversely symmetrical orasymmetrical of the furnace, it will be observed that eiiiux gasescomprising the products of combustion, generated in the partialchambers, must move across the ad-l jacent partitions to exhaust throughthe stacks. This forces the heated gases to scour the work lying in thelots 29 on the rollers on their path toward the vents. Simultaneouslywith the forced exhaust of the gases passing through the vents,

-tion of the work passing therethrough, owing to the simultaneousscouring of the work by the heated gases 'on the sides and upper surfaceof the work. The induced cooling draft mixes with the heated gasespassing up the stack. Under certain controlled conditions'the combustionin the furnace may be partially incomplete so far as concerns gasespassing across the work and up the stack, and the cooling air may beused-to complete the combustion about the work.v

4I, and extending through the top of the furnace,

and, if desired, these stacks may terminate flush with the inner,surface of the top of the furnace chamber at the line 44 spaced fromanges 43 by the roof thickness. The stacks illustrated in these figures(1, 2, and 3) are of refractory materia] such as silicon-carbide orsimilar heatresisting material. The preferred form of stack involves aninternal stack extension 42 of stack 42, extending internally of thefurnace toan intake mouth or entrance opening 45 juxtaposed to the workW, for reasons to be explained. lIt will be understood that however thevents are formed, whether as mere roof openings, short stacks extendingfrom the roof line upwardly, or complete stacks extending axially inboth directions from the roof, the axial center of the vent is disposedgenerally in a transverse diametric plane passing centrally through thespace 22 between the partition walls, and preferably bisecting therespective slots 29. The vents are thus axially juxtaposed in symmetryto the center of the given partitions. In the case of peripherallyoff-set In forming the vents or stacks, itis preferred, as noted. toextend the stacks into the furnace, so as to dispose the entrance mouththereof close to the upper end of the slot 29 so as to force the ventinggases to pass even closer to the work on their path across the partitionand into the open mouth of the stack. Thus, as noted, stacks 42 arecontinued inwardly of the furnace in a preferably integral extension 42'having the inner open mouth 45 in spaced relation to the wall of thefurnace through which it extends. While it will be recognized that theoptimum length of the extension 42' and thus the actual disposition ofthe entrance mouth 45, may vary within a certain range of predeterminedadjustment, the structure is designed to abstract the products ofcombustion from a point or area within the furnace in relative adjacencyto the work. The function is that the point or area of abstraction ofthe-products of combustion be disposed in relative adjaccncy to thework.

It will be seen that there is thus provided a roller hearth furnace ofhigh efficiency in which pieces of work can be fed continuously throughthe furnace supported and conveyed by rollers.

in the furnace, .but which rollers are maintained wat safe heatedconditions by forced external cooling without appreciable adverseeffects on the work and with steady increase of heat investiture alongthe length of the work as it .pro-

gresses.

It will be appreciated that many changes may be made in the furnacewithout departing from the principles of the invention, and such are, ofcourse, to be construed as within the scope of the invention unlessotherwise limited in the hereinafter appended claims. One proposedmodification is disclosed in Figs. 4 and 5 herein. In the form of theinvention of these figures the main body of the furnace and rollers aresubstantially identical with those already described sothat the samereferencecharacters apply and are used threwith. The partial partitionsbetween chambers and the vents, however, are diner-ent. and in place ofa single entrance for the exhaust gases adjacent to the work, twogenerally diametrically spaced entrances adjacent to the sides and uppersurface -of the work are provided. In this form of the device thepartitions and stacks are shown as formed from refractories, andcomprise the transversely extending longitudinally spaced wallsrespectively 46 and 4l, which, with external faces presentinglongitudinally of the furnaces, are continuous from the bottomwall toand through the upper wall I2 of the furnace adjacent to the respectiveside walls i3 and I4 thereof. The respective walls 46 and 41 are spacedin the lower portion to define an air conduit 39 closed,

except toward the center, by a horizontal cross connection 48, analogousin part to the cross connection 2| vof the earlier figures. The crossconnection is cut away inthe substantial center to form the longitudinalslot 50, formed by the lower horizontal surface I in the walls 46 and4l, and the side edge vertical surfaces 52 and 53 of the crossconnection 48, continued vertically and longitudinally of the furnace inthe internal spaced mutually facing walls 54 and 55. merging into theroof of the furnace 'and forming and defining a narrowed portion'of thethrough axial passage 5@ of the furnace in lon-y gitudinal communicationwith the adjacent in- ,complte or partial furnace compartments orchambers defined .by the respective incomplete partitions. The sidewalls il and i4, the cross connection 48, and the walls 54 and 55 definerespectively substantially vertical stacks or vents Iii and 6| leadinginto communication with .the 'slot su and with the air conduit or Chamidas by the respective -exhaust intake openings 62 and 63 respectively.The entrances to the stacks are disposed on opposite sides of the slotin the vicinity of any work W disposed therein and supported on theroller 40.

As, depending upon the vertical dimensions of the elongated work passingthrough the furnace,

the entrances to the Vstacl: are preferably symmetrically and oppositelydisposed below the level of the upper surface of the travelling work, itwill be observed that the eillux gases in the partial chambers must`pass scouringly around and about the work in moving longitudinally ofthe furnace and into the vents. The same accelerations of the exhaustgases and the same injector action in drawing in the cooling stream ofair will maintain, as in the earlier figures.

'I'he rollers will be forcibly cooled by the air inv take. while thespent names will be forced about practically the entire bar or rod beingheated, as it moves between contiguous partial furnace chambers.

It will be understood that the stacks or vents may 'discharge into thefurnace room, or, if desired, be connected to chimneys or other draftcreating evacuation devices, to expedite the controlled flow of thespent gases. It will be understood that suitable conventional dampers orthe like may be associated with any of the vents in order to regulateand control the rate of eiiiux gas flow in accordance with thepredetermined rate and volume of fuel input. and as modified byvariations in masses of the work being heated.

It will be seen that in the forms described hitherto reliance hasibeenmade upon the induction of a draft by the etiiux velocity of the spentgases passing up the respectivestacks. While in general this iscompletely adequate, it will be seen that this cooling flow can beaugmented to ad vantage under certain demands by the modifica- 5 tionshown in Figs. 6 and 7. In this form of the invention the parts are allsubstantially similar to the disclosures of either Pigs. l, 2, and 3, orof Figs. 4 and 5. and illustrativeiy they are like the latter, so far asthe furnace structure is concerned. However, the partitions of thelatter, in place of being in free communication with the outer air. areclosed transversely and vertically by the transverse ducting elements l!effectively closing the lower edge of the slot 29 except for the conduit66 which leads to the blower $1, power driven to force a stream of airfrom outside ofthe furnace into and through the slot 29. Preferably, theflow through the conduit 66 is controlled by a damper Il positioned by acontrol device 10, to regulate the flow within close limits to accordwith the instant demand at the particular roller 40. It will beunderstood that the ducting mentioned may be actual metal or likeinserts, or may simply be the boundary surfaces of refractory materialso placed as to denne the conduit, or part thereof, and thecommunication with the lower end of an otherwise closed slot 29.Obviously, the passage of the roller 40 through the ducting will requirea small clearance to permit rotation thereof without frictional contactwith such ducting. The advantages of the forced draft for cooling willbe apparent.

I claim as my invention: A

l. Aroller hearth continuous integral furnace comprising a furnacechamber, partition means in the chamber defining a cooling air conduit,a roller mounted in the furnace chamber juxtaposed to said partitionsubstantially in the path of cooling air passing through said conduitmeans for directing a cooling air stream from the conduit externallyabout said roller and means juxtaposed to'said conduit for venting gasesfrom the chamber.

2. A roller hearth continuous integral furnace comprising a furnacechamber. partition means Y extending transversely of the chamber anddefining a cooling air conduit, a roller mounted in said partition meansin said conduit, said parti- 50 tion means 'providing a clearanceadjacent to said roller to permit elongated work to rest upon saidroller, a vent for the furnace chamber disposed in general verticalalignment with the partition means so that spent gases passing into 55said vent must pass across said partition means in incidence with thework passing across said partition means supported on said roller so asto induce a cooling airflow from said channel against said roller.

60 -3. A roller hearth continuous integral furnace 'comprising a furnacechamber, a plurality of partition means extending transversely of thechamber in longitudinally spaced relative dispositions, each partitionmeans having an internal space, a roller disposed in said space, a ventin the chamber in substantial vertical alignment with a partition meansand juxtaposed to the path of the work so that gases passing into saidvent must scour the work passing across the in- 70 stant partitionmeans.said vents being respectively substantially vertically aligned with saidpartition means.

' 4. A roller hearth continuous integral furnace comprising a furnacechamber, partition means 75 in said chamber to define a plurality ofpartial combustion chambers, rollers associated with the partition meansbetween combustion chambers, vents in the furnace chamber betweencombustion chambers, and means associated with the partitions definingair conduits for externally cooling said rollers, said Ventsrespectively substantially vertically aligned with said partition means.

5. A roller hearth furnace comprising means defining a furnace chamber,a plurality of rollers mounted in the chamber and extending transverselythereof, a vent for products of combustion in general' axialintersection with the axis of each of the respective rollers, shieldingmeans comprising generally parallel spaced walls extending transverselyof the chamber on both sides of each roller to shield same and to definea plurality of partial combustion chambers in the furnace chamber, meansfor heating the combustion chambers, and means associated with therespective shielding means for establishing communication betweenexternal air and the rollers to cool the latter.

6. A roller hearth furnace comprising means defining an elongatedfurnace chamber, a partial partition extending transversely of thechamber and comprising internally a vertical air channel and externallypartition surfaces between contiguous partitionspaced partial combustionchambers in the furnace chamber, means for heating the combustionchambers, a vent in the furnace chamber substantially over saidpartition, and a roller disposed in said channel.

7. A roller hearth furnace as described in claim 6 characterized by thefact that the vent has an intake mouth disposed inwardly of the meansdefining the chamber.

8. A roller hearth furnace comprising walls defining an elongatedfurnace chamber, a partition extending transversely and vertically ofthe chamber from the lower Wall thereof to define an air conduit passingthrough the side walls thereof, a slot in said partition axial of thechamber, a roller mounted for rotation in the conduit having a surfacein said slot to receive and support work out of contact with saidpartition, means for heating the chamber, and a vent for spent gaseshaving an entrance substantially juxtaposed to said slot.

9. A roller hearth furnace comprising upper .lateral and lower wallsdefining an elongated furnace chamber, a partition device extendingtransversely of the chamber between lateral walls and the lower wall todefine partial combustion chambers spaced apart axially of the furnacechamber by the device, said device comprising spaced walls merging intothe walls dening the sides and bottom of the furnace chamber to define aconduit for cooling air which passes through the lateral walls of thefurnace chamber, said spaced walls 50 of the device having registeringhorizontal openings to define a slot, means closing the space betweenthe walls of the device on each side of said slot to define an outletfor the cooling air conduit within the furnace, roller means mounted fordriven rotation in the space between the walls of the device having awork supporting and conveying peripheral edge thereof exposed withinsaid slot and said outlet, and vent means in the furnace chamber ingeneral alignment with the partition device so that efflux gasesentering said vent means from the partial combustion chambers musttraverse the partition means.

10. A roller hearth furnace as described in claim 9 characterized by thefact that the vent means comprises a stack having an entrance mouthwithin the furnace chamber.

11. A roller hearth furnace as described in claim 9 characterized by thefact that the vent means comprises a plurality of vents each alignedgenerally with the partition device.

l2. A roller hearth furnace as described in claim 9 characterized by thefact that the vent means comprises a plurality of transversely spacedvent devices each having entrance mouths within the furnace chamber inrespective juxtaposition to said outlet.

13. A roller hearth continuous integral furnace comprising a furnacechamber, partition means in the chamber defining a cooling air conduit,a. roller mounted in the furnace chamber juxtaposed to said partition,said partition having a constricted outlet forming mean for directing acooling air stream from the conduit externally about said roller, ventmeans in the upper portion of the chamber and power means for forcingcooling air to the constricted outlet.

14. A roller hearth continuous lintegral furnace comprising a furnacechamber, a plurality of partition means extending transversely of thechamber in longitudinally spaced relative dispositions, each partitionmeans having an internal space, a roller disposed in said space, a ventin the chamber in substantial alignment with a partition means andjuxtaposed to the path of the work so that gases passing into said ventmust scour the work passing across the instant partition means, andpower driven means for forcing cooling air through the meansestablishing communication. 15. A roller hearth furnace comprising meansdefining a furnace chamber, a plurality of rollers mounted in thechamber and extending transversely thereof, a vent for products ofcombustion in general axial intersection with the axis of each of therespective rollers, shielding means comprising generally parallel spacedwalls extending transversely of the chamber on both sides of each rollerto shield same and to denne a plurality of partial combustion chambersin the furnace chamber, means for heating the combustion chambers, meansassociated with the respective shielding means for establishingcommunication between external air and the rollers to cool the latter,and means for forcing cooling air through the means establishingcommunication.

SAMUEL M. STOLER.

REFERENCES CITED The following references are of record in the file ofthis patent:

i UNITED STATES PATENTS {Number Name Date g5 1,946,971 Harter Feb. 13,1934 FOREIGN PATENTS Number Country Date 139,099 Austria. May 15, 1934

